Running Rough, won't idle...all of a sudden

[streetstang67]

Went to take the stang out yesterday and it was hard to start (backfired) and won't idle unless i held it to at least 1200 rpm. Also, when I took it out, its running rough, rpms surging up and down while cruising. The car was running fine last week.

I've checked the powervalve and looked over for vacuum leaks. Thats all fine.
I've refueled, to make sure it wasn't bad gas...no change.
Fuel seems to be flowing in fine, I can see through the clear fuel filter.
I changed the spark plugs (been needing to anyway)...no change.
I hooked timing light up to all plug wires to make sure they were getting power.

I'm running out of options, other than starting to replace things like the coil, carb, etc.... Any suggestions?

Thanks

 

[woodsnake]

Slipped timing gear?

 

[streetstang67]

Timing seems fine, it won't idle down low enough to check it, but twisting the distributor doesn't help anything.

Changed the coil, in will now idle, but barely...cuts out when i put it in gear.

I'm thinking about a carb rebuild, any other suggestions?

 

[SScott]

I know this is not the same issue you are having but close and maybe a start for you to look. I bought a new Pro-Form body and after installing, my car did the exact same thing. After hours of trying to figure it out, I discovered the plumbing to the air bleeds were never drilled... so, maybe your air bleeds have some trash in them? I would do the carb rebuild like you said and take a rubber tipped blow gun to every orifice.

Hope you get it going.

 

[Tim65GT]

It sound like a vacuum leak. My recent experience with this same issue was bad intake gaskets. I verified it by spraying carb cleaner around and the idle increased when I hit the leaks.

Spray around your carb and gaskets, and see if your rpm goes up.

 

[tx65coupe]

Thats a good idea, but wouldn't the carb cleaner make the idle go down?

 

[68RCodeConv]

Thats a good idea, but wouldn't the carb cleaner make the idle go down?

It is a highly flammable substance so when the motor sucks it in the engine speed picks up. Same thing with propane out of an unlit propane torch.

 

[streetstang67]

I agree it sounds like a vacuum leak, but I couldn't find any. I'll try the intake gaskets...hopefully i'll find something....

 

[bocksta]

If you have a vacuum gauge you could use this.

thats the best image i have of it. Good luck.

 

[hardsy]

Possibly check the the pcv valve.

 

[tx65coupe]

It is a highly flammable substance so when the motor sucks it in the engine speed picks up. Same thing with propane out of an unlit propane torch.

Everytime I have sprayed carb cleaner into a carb while its running begins to stall.

 

[Tim65GT]

Everytime I have sprayed carb cleaner into a carb while its running begins to stall.

Come to think of it, it wasn't carb cleaner I used, I was out. I think it was brake cleaner.

 

[j69302]

Everytime I have sprayed carb cleaner into a carb while its running begins to stall.

dont spray it into the carb, spray it around the gaskets and seals of the intake manifold and carb base.

 

[tx65coupe]

I guess spraying in the carb versus just in the intake could produce different results. Its interesting that it will make the idle go up. Thats good to know.

 

[D.Hearne]

Everytime I have sprayed carb cleaner into a carb while its running begins to stall.

That's because you sprayed too much into it. I was working on a Briggs & Stratton the other day and ran it on only carb cleaner just by spraying.

 

[D.Hearne]

Went to take the stang out yesterday and it was hard to start (backfired) and won't idle unless i held it to at least 1200 rpm. Also, when I took it out, its running rough, rpms surging up and down while cruising. The car was running fine last week.

I've checked the powervalve and looked over for vacuum leaks. Thats all fine.
I've refueled, to make sure it wasn't bad gas...no change.
Fuel seems to be flowing in fine, I can see through the clear fuel filter.
I changed the spark plugs (been needing to anyway)...no change.
I hooked timing light up to all plug wires to make sure they were getting power.

I'm running out of options, other than starting to replace things like the coil, carb, etc.... Any suggestions?

Thanks

Got Points ? If you do, then they're a likely culprit. Might be the vacuum advance diaphram also ruptured and the timing's off due to it.

 

[streetstang67]

Thanks for the feedback...

PCV valve is fine...also, no points, I have the crane xr-i electronic ignition. I rebuilt the carb saturday and that didn't change anything. Also took valve covers off to see if anything looked odd, everything seemed fine. Used the timing light on each plug wire to make sure they were all getting spark, they were. Fuel pump is holding steady around 4 psi, I assume thats high enough...man this is frustrating, running out of options.